From d9753155ae76996834dd370f76d9a28867ed844f Mon Sep 17 00:00:00 2001
From: Mykhailo Chalyi <mike@chaliy.name>
Date: Fri, 13 Mar 2026 00:40:27 +0000
Subject: [PATCH] fix(security): sanitize reqwest error messages to prevent
 hostname leakage

from_reqwest() was passing raw reqwest error strings through
RequestError(err.to_string()), which could contain internal hostnames
or URL details. Now classifies errors by kind (redirect, body, decode)
with generic messages.

Closes #38
---
 crates/fetchkit/src/error.rs           | 10 +++++-
 crates/fetchkit/tests/ssrf_security.rs | 45 ++++++++++++++++++++++++++
 specs/threat-model.md                  |  6 ++--
 3 files changed, 58 insertions(+), 3 deletions(-)

diff --git a/crates/fetchkit/src/error.rs b/crates/fetchkit/src/error.rs
index 5642004..05e5a7b 100644
--- a/crates/fetchkit/src/error.rs
+++ b/crates/fetchkit/src/error.rs
@@ -61,13 +61,21 @@ pub enum FetchError {
 
 impl FetchError {
     /// Create an error from a reqwest error
+    ///
+    // THREAT[TM-LEAK-001]: Sanitize reqwest errors to avoid leaking internal hostnames/IPs
     pub fn from_reqwest(err: reqwest::Error) -> Self {
         if err.is_timeout() {
             FetchError::FirstByteTimeout
         } else if err.is_connect() {
             FetchError::ConnectError(err)
+        } else if err.is_redirect() {
+            FetchError::RequestError("redirect error".to_string())
+        } else if err.is_body() {
+            FetchError::RequestError("error reading response body".to_string())
+        } else if err.is_decode() {
+            FetchError::RequestError("error decoding response".to_string())
         } else {
-            FetchError::RequestError(err.to_string())
+            FetchError::RequestError("request failed".to_string())
         }
     }
 }
diff --git a/crates/fetchkit/tests/ssrf_security.rs b/crates/fetchkit/tests/ssrf_security.rs
index b3383aa..7003e90 100644
--- a/crates/fetchkit/tests/ssrf_security.rs
+++ b/crates/fetchkit/tests/ssrf_security.rs
@@ -458,3 +458,48 @@ async fn test_input_007_subdomain_not_matched_by_host_prefix() {
     let result = tool.execute(req).await;
     assert!(!matches!(result, Err(FetchError::BlockedUrl)));
 }
+
+// ============================================================================
+// TM-LEAK-001: Error messages must not leak internal hostnames or IPs
+// ============================================================================
+
+#[test]
+fn test_leak_001_request_error_variants_are_generic() {
+    // THREAT[TM-LEAK-001]: Verify all RequestError messages are generic and
+    // don't leak hostnames or IPs from reqwest errors.
+    // The from_reqwest fallback classifies by error kind, not raw message.
+    let generic_messages = [
+        "redirect error",
+        "error reading response body",
+        "error decoding response",
+        "request failed",
+    ];
+    for msg in &generic_messages {
+        let err = FetchError::RequestError(msg.to_string());
+        let display = err.to_string();
+        assert!(
+            !display.contains("127.0.0.1"),
+            "Error should not contain IPs: {display}"
+        );
+        assert!(
+            !display.contains("internal"),
+            "Error should not contain hostnames: {display}"
+        );
+    }
+}
+
+#[test]
+fn test_leak_001_timeout_and_connect_display_are_generic() {
+    // Verify that timeout and connect error Display messages are static
+    // strings that don't contain any dynamic content
+    let timeout_msg = FetchError::FirstByteTimeout.to_string();
+    assert_eq!(
+        timeout_msg,
+        "Request timed out: server did not respond within 1 second"
+    );
+
+    // ConnectError uses "Failed to connect to server" as Display, hiding
+    // the reqwest source error from the user-facing message
+    let blocked_msg = FetchError::BlockedUrl.to_string();
+    assert_eq!(blocked_msg, "Blocked URL: not allowed by policy");
+}
diff --git a/specs/threat-model.md b/specs/threat-model.md
index ebe076c..ac1618c 100644
--- a/specs/threat-model.md
+++ b/specs/threat-model.md
@@ -284,8 +284,10 @@ against unbounded responses (TM-DOS-001).
 
 **TM-LEAK-001 — Error message detail (MITIGATED):**
 FetchKit's error types (`FetchError`) use generic messages that don't include
-resolved IP addresses. Connect errors say "Failed to connect to server" without
-revealing the specific IP or port that was attempted.
+resolved IP addresses or internal hostnames. Connect errors say "Failed to connect
+to server" and the `from_reqwest()` fallback path classifies errors by type
+(redirect, body, decode) instead of passing through raw reqwest error strings
+which could contain hostnames or URL details.
 
 ## 6. Content Conversion (TM-CONV)